Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
  • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
  • B29C35/08—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
  • B29C44/34—Auxiliary operations
  • B29C44/3415—Heating or cooling
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
  • B29C44/34—Auxiliary operations
  • B29C44/56—After-treatment of articles, e.g. for altering the shape
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
  • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
  • B29C35/08—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation
  • B29C35/0805—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation
  • B29C2035/0855—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould by wave energy or particle radiation using electromagnetic radiation using microwave
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C35/00—Heating, cooling or curing, e.g. crosslinking or vulcanising; Apparatus therefor
  • B29C35/02—Heating or curing, e.g. crosslinking or vulcanizing during moulding, e.g. in a mould
  • B29C35/12—Dielectric heating
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29K—INDEXING SCHEME ASSOCIATED WITH SUBCLASSES B29B, B29C OR B29D, RELATING TO MOULDING MATERIALS OR TO MATERIALS FOR MOULDS, REINFORCEMENTS, FILLERS OR PREFORMED PARTS, e.g. INSERTS
  • B29K2033/00—Use of polymers of unsaturated acids or derivatives thereof as moulding material
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S521/00—Synthetic resins or natural rubbers -- part of the class 520 series
  • Y10S521/915—Utilizing electrical or wave energy during cell forming process

Definitions

• the present invention relates to a method for making a rigid foam article by prewarming a rigid heat-foamable synthetic resin until at least a portion of the resin surface is softened and then initiating the foaming process by further heating with microwave or high-frequency radiation.
• the prewarmed synthetic resin is a copolymer comprising at least 80 percent by weight of units of acrylic acid or methacrylic acid and of acrylonitrile or methacrylonitrile, together with a blowing agent. On heating, acrylimide or methacrylimide groups are formed from the acid and nitrile groups.
• uniform foam slabs are obtained in a microwave or high-frequency field if a rigid slab of foamable synthetic resin is preheated until at least a portion of its surface is at or above the softening temperature of the resin and the microwave or high-frequency field initiating the foaming process is then allowed to act on the slab until foaming occurs. It is important that a microwave or high-frequency field of an intensity that will induce foaming not be allowed to act on the foamable synthetic resin slab until at least a portion of its surface has been thermally softened. How it is heated is not important so long as this condition is satisfied. If preheating is effected by means of a microwave or high-frequency field, its intensity must be such that foaming will not set in.
• softening temperature is meant that temperature at which the synthetic resin elastically expands under the foaming pressure without fracturing.
• the temperature at which this condition occurs may be exceeded, but preferably not to the extent that the temperature region of plastic deformability is reached.
• any heat source with which the softening temperature can be reached at the surface is suitable for the preheating of the foamable synthetic-resin slab.
• an air oven in which an appropriately heated atmosphere, usually air, will act on the surface of the slab may be employed, or the slab surface may be exposed to heat radiation. Heating by heat transfer from a liquid medium or a hot solid surface is also possible but is usually less convenient.
• microwave fields or high-frequency fields can be used for preheating, alone or together with the other heat sources mentioned, provided that care is taken that foaming is not prematurely induced in the interior.
• a field of appropriately low intensity may be used or the field may be allowed to act on the slab only momentarily or intermittently.
• the microwave or high-frequency field adapted to induce foaming can be cut in. This is preferably done only when the surface of the synthetic resin slab has been heated completely or almost completely to or above the softening temperature. It is not detrimental if foaming has already set in at the surface. Further heating to foaming temperature is faster than with any other heat source acting only externally.
• Microwave ovens which are suitable for use in the method of the invention are known in the art, where they are employed for drying, for example. They operate with wavelengths ranging from 1 to 50 cm. The most commonly used wavelength is 12.3 cm, which corresponds to 2450 MHz.
• the radiation or field is produced by a so-called magnetron and is distributed in the microwave oven as uniformly as possible. The more uniform the field, the lower the danger that isolated foaming zones will form that are not associated with a softened surface zone.
• the power output of the microwave generator will, of course, have to be based on the size of the synthetic resin slab to be foamed and on the foaming temperature required.
• High frequency generators suitable for use in the method of the invention operate at wavelengths ranging from 1 to 50 meters.
• a commonly used wavelength is 11 meters, which corresponds to 27.12 MHz.
• Such generators are employed to heat-seal plastics and to foam wetted polystyrene beads.
• Kunststoff-Physik im Gespraech (“Discourse on the Physics of Synthetic Resins"), a publication of BASF AG, 1969, p. 179.)
• a field distribution that is as uniform as possible will be advantageous.
• a material In order that a material may be heated in a microwave or high-frequency field, it must be capable of absorbing the respective radiation. That will be the case of the material contains a sufficient number of polar structures. Such structures may be a constituent of the polymer molecules which make up the synthetic resin or they may be contained in low molecular weight substances, such as water or formamide, admixed with it. Synthetic resins having polar structures include those which contain carbonyl, carboxyl, hydroxyl, halogen, amino, or carboxylamido groups.
• synthetic resins containing a copolymer comprising at least 80 percent by weight of units of acrylic acid or methacrylic acid and of acrylonitrile or methacrylonitrile are suitable for use in the method of the inventions.
• the polymer should comprise at least 20 percent by weight of acrylic acid or methacrylic acid.
• the ratio by weight of acrylic acid and/or methacrylic acid to acrylonitrile and/or methacrylonitrile is from 3 : 2 to 2 : 3.
• the copolymer may contain up to 20 percent by weight of other ethylenically unsaturated monomers copolymerizable therewith, for example acrylamide and methacrylamide, styrene, lower alkyl (C 1 -C 4 ) esters of acrylic acid and methacrylic acid, as well as up to 5 percent by weight of crosslinking monomers having 2 or more polymerizable double bonds, such as esters of acrylic acid and methacrylic acid with polyols (e.g. glycol dimethacrylate), divinylbenylene, triallyl cyanurate, and methylene-bis-acrylamide.
• polyols e.g. glycol dimethacrylate
• divinylbenylene divinylbenylene
• triallyl cyanurate methylene-bis-acrylamide
• metal salts of acrylic acid and methacrylic acid may be present in amounts up to 5 percent by weight, particularly salts of polyvalent metal ions such as Mg 2+ , Zr 4+ , Cr 3+ , Co 2+ , Zn 2+ , Cd 2+ , Bi 3+ , TiO 2+ , and Pb 2+ .
• These synthetic resins soften at from 140° C. to 150° C. and start to foam from 160° C. to 180° C.
• a reaction of polymerized units of acrylonitrile or methacrylonitrile and units of acrylic or methacrylic acid takes place to form units of acrylimide or methacrylimide. Foamed plastics based on polymethacrylimide have acquired considerable commercial importance.
• such resins also comprise from 2 to 15 percent, preferably 2 to 10 percent, by weight of a blowing agent which on being heated yields a gas or vapor.
• a blowing agent which on being heated yields a gas or vapor.
• Formamide, monomethyl formamide, urea, water, and lower aliphatic alcohols are illustrative of such blowing agents, which are well known in the art.
• Slabs of such a synthetic resin having a thickness of from 1 to 4 cm, for example, are best heated in a circulating air oven at 170° C. to 200° C. until the surface softens and are then exposed to a microwave field. Preheating usually takes from about 5 to 30 minutes, while the microwave treatment requires somewhat less time. By contrast, when foaming is effected by the use of hot air alone, a foaming time of about 2 hours is required.
• a slab measuring 70 ⁇ 70 ⁇ 23 mm of a rigid foamable synthetic resin having a softening temperature of 160° C. and containing a copolymer of methacrylic acid and methacrylonitrile in a molar ratio of 3:2 together with 8 percent, by weight of the polymer, of a blowing agent mixture of formamide and tert.-butanol was preheated in a hot air oven to an approximately uniform surface temperature of 160° C. within 30 minutes and then treated for 6 minutes with a microwave field whose power was controlled through an operating cycle of 10 seconds of radiation followed by a 50-second pause.
• a foam slab naming a density of 38 kg/m 3 was so obtained.
• the microwave oven employed (Sharp Model R 8000 E) had a power consumption of 1.4 kw in the hot air section and of 1.3 kw in the microwave section, with a power output of 650 watts with a 2-liter water load, and had been retrofitted to permit simultaneous microwave and hot air operation. This made it possible to carry out the entire foaming operation in the same unit using only hot air during the preheating time and then cutting in microwave heating for foaming.
• a slab measuring 120 ⁇ 120 ⁇ 23 mm of a rigid foamable synthetic resin having a softening temperature of 180° C. and containing a weakly crosslinked copolymer of methacrylonitrile and methacrylic acid in the aforementioned molar proportions and 10 percent, by weight of the polymer, of a blowing agent mixture of formamide and tert-butanol was preheated for 30 minutes in a hot air oven to an approximately uniform surface temperature of 180° C.
• the preheated slab was placed between the electrodes if a high frequency furnace (Model HGV 4001 of the firm Herfurth GmbH) having a useful output of 4 kw at a frequency of 27.12 MHz.
• the electrodes measured 400 ⁇ 400 mm.
• a monomer mixture comprising:
• the prewarmed piece was foamed in 5-7 minutes in a high frequency field as in Example 2, during which 50 percent of maximum output was intermittently applied.

Landscapes

• Health & Medical Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Toxicology (AREA)
• Physics & Mathematics (AREA)
• Oral & Maxillofacial Surgery (AREA)
• Thermal Sciences (AREA)
• Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)
• Molding Of Porous Articles (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=6309364

Family Applications (1)

Country Status (5)

Cited By (15)

Families Citing this family (17)

Citations (2)

Family Cites Families (4)

• 1986
  • 1986-09-11 DE DE19863630930 patent/DE3630930A1/de not_active Withdrawn
• 1987
  • 1987-08-27 EP EP87112433A patent/EP0259706B1/de not_active Expired - Lifetime
  • 1987-08-27 DE DE8787112433T patent/DE3762324D1/de not_active Expired - Lifetime
  • 1987-08-27 ES ES87112433T patent/ES2016601B3/es not_active Expired - Lifetime
  • 1987-09-02 US US07/091,970 patent/US4740530A/en not_active Expired - Fee Related
  • 1987-09-10 JP JP62225461A patent/JPS6374629A/ja active Pending

Patent Citations (2)

Also Published As

Similar Documents

Legal Events